The present invention relates generally to amplifier circuits, and more specifically to amplifier circuits for high frequency operation having a wide input range.
Low noise amplifier (LNA) that use differential amplifiers are often used in high performance analog and mixed-signal integrated circuits, as part of a buffer or gain block. An output of a differential amplifier is a measure of the difference between a pair of input signals, so that if the differential amplifier is made of matched transistor devices (e.g., ones that are structural replicates of each other and, accordingly, exhibit very similar DC and AC electrical characteristics), then common mode noise occurring at the inputs of the amplifier or the power supply is significantly reduced at its output. The difficulty in designing a multi-band LNA circuit comes from the fact that it has to provide different functions at different operating frequencies. Therefore, to design a multi-band amplifier, it must satisfy different operating bandwidths at different standards. In order to meet the trends of increasingly standards, the operation bandwidths and gain flatness performance of the multi-band LNA must be improved. The amplifier must be able to provide input matching, wide-band interference rejection and maximum gain flatness performance. However, conventional LNAs can not meet the required of multi-standard function or wide-band solution.
Thus, a critical need is prevalent for apparatus, systems and methods that enable differential amplifiers, especially when used in LNAs, to overcome at least the gain flatness limitations that limit the suitability to wideband applications.
It will be appreciated that for simplicity and clarity of illustration, elements illustrated in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements are exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals have been repeated among the figures to indicate corresponding or analogous elements.